1. Field of the Invention
The invention is concerned with an improvement in a fluid controller. More particularly, the invention is concerned with an improvement in a dual acting hydraulic device which controls flow to a balanced cylinder of a power steering system. The improvement relates to means for preventing overshoot of a spool valve portion of such a fluid controller by provision of a dash pot which linearly dampens the motion of said spool valve and resulting serious vibratory instability in the motion of a vehicle using such a fluid controller in its power steering system.
2. Prior Art
A number of hydraulic devices are known for providing power steering for vehicles. Typical such devices are discussed for example in "HGA Hydrostatic Steering System, Hydraguide (Trademark of TRW Inc.) Ross Engineering & Service Manual", Manual No. HGA-200, TRW Inc. 1971 and in U.S. Pat. Nos. 3,288,034; 3,385,057 and 3,452,543. The devices taught by the above manual and patents are essentially of the gerotor type and have advantageously been used to provide power steering for a number of vehicles along with manual steering if the main fluid pump supplying fluid thereto is inoperative.
A particular problem of vibratory instability due to overshoot of the spool valve of the gerotor type devices has been discovered when utilizing these prior art gerotor devices. This problem is especially magnified in systems wherein the hydraulic flow rates are especially great as for example in off-road vehicles and other especially heavy duty equipment as is used in the construction industry. With the greater flow rates which occur within the hydrostatic power steering devices used in such systems, it has been found that the instability which occurs therein is multiplied in effect to cause very significantly erratic and continuing vibratory motion of the vehicles using such devices. With smaller vehicles where lower flow rates occur within the power steering hydraulic controller, instability still occurs but motion resulting therefrom is less erratic because of the lesser flow forces created in the system.
Attempts to solve this problem by frictional dampening of the spool valve have been found by us to cause higher wheel effort, increased operating temperatures and failure of the spool valve to return to its centered position.
It would be highly advantageous to provide a straight forward and inexpensive improvement in a gerotor hydraulic device useful for power steering purposes such as those taught in the above mentioned manual and patents whereby such a hydraulic controller device could be used in heavy duty equipment such as off-road vehicles and the like and wherein erratic motion would be prevented in a smooth working, low noise, low cost device. The present invention provides just such an improvement.